1. Technical Field
The present application relates to an image processing apparatus, an image forming apparatus, an image processing method, and a recording medium in which a watermark for copy control and a predetermined pattern that is used for restricting a copy of an image are allowed to be added to image data.
2. Description of the Related Art
In the prior art, for the purpose of easily checking document originality whether a document is not forged by copying, a watermarking for copy control technique is known (see Japanese Patent Application Laid-Open No. 2007-88763). In the watermarking for copy control technique, for example, printing is performed in a state that a dot pattern (a watermark for copy control) designed such that a text or a pattern embedded in advance in a document becomes visible when the document is copied is added to the image data serving as a printing target. Patent Document 1 discloses a configuration that a watermark is added when image data is printed. Further, a function of copy with the watermarking for copy control is also known in which image data obtained by reading a document through an image reading apparatus is printed in a state that the watermark is added.
Further, as a technique different from the watermarking for copy control technique, for example, a technique is known that a copy of a document is inhibited by using a copy inhibition pattern (see Japanese Patent Application Laid-Open No. 2007-135091). In this technique, for example, at the time of printing, image data is printed in a state that a specific pattern defined in advance as the copy inhibition pattern is added. Then, at the time of copying a document generated in this way, the presence or absence of the specific pattern is detected in the read-out image data. Then, when the specific pattern is detected, copy processing is stopped.
Such a technique employing the copy inhibition pattern is effective in a multi-function peripheral provided with the function of detecting the copy inhibition pattern and then inhibiting the copy of the document. Nevertheless, a problem arises that the copy of the document is not inhibited in a multi-function peripheral not provided with such a function.
On the other hand, in the watermarking for copy control technique, the image reading apparatus need not be provided with a special detection function. Thus, the watermarking for copy control technique is effective in an arbitrary multi-function peripheral. Nevertheless, in the watermarking for copy control technique, forced inhibition of the copy of a document achieved in the technique employing the copy inhibition pattern is difficult to be achieved. That is, its effect is merely a warning.
As such, the watermarking for copy control technique and the technique employing the copy inhibition pattern have different features and disadvantages from each other, and are complementary to each other. Thus, an approach for complementing their disadvantages is that the watermarking for copy control technique and the technique employing the copy inhibition pattern are employed simultaneously.
Nevertheless, the watermark is composed of a dot pattern. Thus, when the copy inhibition pattern is composed of a dot pattern similarly to the watermark, the two patterns interfere with each other. This causes a problem that the accuracy is seriously degraded in detecting the copy inhibition pattern from image data read from a document at the time of copy of the document. In particular, in a case that the watermark and the copy inhibition pattern are processed individually by separate modules and that change of the relative positions of the two patterns is not allowed, this problem becomes more serious.
For the purpose of resolving such a problem, Japanese Patent Application Laid-Open No. 2008-244699 discloses a method that the watermark is deleted partly. Nevertheless, in the method disclosed in Japanese Patent Application Laid-Open No. 2008-244699, the contrast increases between the part where the watermark is still present and the part where the watermark has been deleted. This causes a problem that the foreground image (the original image before the watermark is added) becomes difficult to be seen. Here, the watermark is embedded in the background of a document so as to be used for inhibiting copying. Thus, the degradation in the visibility of the image in the foreground caused by the watermark is a large problem.
Further, the watermark has a type that an illegal copy warning text contained in the watermark becomes visible when copied and a type that the illegal copy warning text becomes invisible. In the illegal copy warning text of visible type, the background region of the watermark is composed of small dots. In the illegal copy warning text of invisible type, the background region of the watermark is composed of large dots. The large dots easily interfere with the copy inhibition pattern. Further, in the illegal copy warning text of invisible type, the region of large dots becomes large. Thus, special consideration is necessary when the watermark including the illegal copy warning text of invisible type is used.